A radiation imaging system, for example, an X-ray imaging system as used in the medical field using X-rays is widely known. Such X-ray imaging system comprises an X-ray source for emitting X-rays to an object to be imaged, an X-ray detector for detecting X-ray radiation passing through the object, and a control device for controlling the operation of the X-ray source and the X-ray detector.
WO 2006/046206 A1 discloses a portable X-ray detector unit comprising a portable, hand-held X-ray detector i.e. a cassette having a plurality of exposure detection fields for measuring the level of radiation to which the object to be imaged is exposed. The portable X-ray detector incorporates automatic exposure control (AEC) for terminating X-ray radiation supply to the object upon determination that the level of X-ray exposure exceeds a predetermined threshold. A user-interface is provided to control the AEC.
DE 10 2005 002983 A1 discloses an X-ray detector system comprising a sensor for registering the start of an X-ray exposure, wherein the X-ray detector is activated in response to the output of said sensor.
US 2012/0082294 A1 discloses an X-ray system comprising a sensor configured to sense a condition that results from an operation of the X-ray tube, wherein the output of the sensor is communicated to an X-ray detection panel.
It has recently been proposed to introduce an exposure detection system wherein the X-ray detector itself can detect the beginning of an exposure of radiation to the object to be imaged. However, this system can be further improved. For example, in case a relatively small area is being exposed and/or a low exposure rate is applied, the X-ray detector may not properly detect the beginning of an X-ray exposure.